In pathological diagnosis, first, after processing of dehydrating the obtained tissue so as to be fixed and blocking with paraffin, the above is cut into thin pieces with a thickness of 2 to 8 μm, the paraffin is removed, and the above is stained to observe with a microscope. The pathologist performs diagnosis based on morphologic information such as change in size and shape of a nucleus of a cell, change in pattern as a tissue, etc., and stain information in the microscopic image. Methods known as the tissue staining method used in pathological diagnosis include a conventional chromatic staining method (for example, Hematoxylin and Eosin staining; hereinafter referred to as HE staining) and a chromatic staining method using enzyme (for example, DAB (diaminobenzidine) staining).
In pathological diagnosis, specifying the protein overexpressing in the tissue slice and its expression amount may be very important information for prognostic expectation and determining the future treatment plan.
For example, HER2 protein coding HER2 gene is a receptor type glycoprotein which penetrates the cell membrane, is composed of 3 domains which are extracellular, transmembrane, and intracellular, is activated by phosphorylating of tyrosine residue when bonded with a growth factor, and is said to be involved in proliferation and malignant alteration of cells through signaling pathways. Overexpression of HER2 protein can be seen in breast cancer, lung cancer, colon cancer, stomach cancer, bladder cancer, etc.
HER2 protein is considered to be a prognostic factor of breast cancer, and it is known that especially in a case where lymph node metastasis is positive, the prognosis of cases where HER2 is positive is significantly poor. HER2 protein is also gathering attention as an information factor for deciding adaptation of a molecularly targeted drug (trastuzumab) and as a result prediction factor of anticancer drugs such as anthracycline type, taxane type, etc.
Typically, overexpression of HER2 protein is examined by an immunohistochemical method (IHC method) and overexpression of HER2 gene is examined by FISH method. According to the HER examination guideline, first, positive, negative, boundary region is discriminated by a simple IHC method, and when the result is positive, it is decided that trastuzumab is provided. When the result is in the boundary region with the IHC method, further examination is done to discriminate positive and negative by the FISH method.
Comparing the IHC method and the FISH method, the IHC method is easier, but there is the problem that accuracy is low. Turning to the FISH method, the accuracy is high, but the process is troublesome, and the cost is high. In other words, there are needs for development of a method of an IHC method which has the same accuracy as the FISH method. Moreover, there are needs for development of a method where the dependence on the person is low and which can be automated.
For example, Patent Document 1 describes a system where a cell nucleus is extracted from an image of biological tissue stained by the DAB method, a cell membrane is specified from an image of biological tissue based on the cell nucleus, a stained state of a cell membrane is determined, and expression of HER2 protein is evaluated based on the result of determination.